Welcome to version 3.0 of the Forensic Photoshop blog - now the Forensic Multimedia Analysis blog. With the latest developments in purpose built software and hardware for the analysis of multimedia, we move the discussion beyond a single piece of software to include all the major developers, image processing fundamentals, court cases, upcoming training offerings, and product reviews.

Monday, March 23, 2009

Bit depth

I'm back from the NATIA conference and will (hopefully) get to everyone's e-mails.

The term "bit depth" is used to describe the number of possible colour values a pixel can have. This concept confuses some folks and I tend to get a quite a few questions from folks who have trouble grasping this rather obscure topic.

Here's a way of thinking about it:

Bit depth = 1

Two possible values: black/white

Bit depth = 8

2 to the 8th power = 256

When you come across a different bit depth, think 2 to the power of the number of bits and you'll have an easy way of figuring out the number of possible values.

Here's a quick quiz. How many possible colour values for a bit depth of 12? Now, how many for 12 bits per channel RGB? If you are shooting in RAW, and your images are 12-14 bpc - would you want to try to cram that info into an 8bpc RGB image out of the gate? Most assign the image a 16 bpc working space in ACR and give the image some head room.

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If you've made it down this far, thank you. It is my pleasure to host this discussion on the forensic video and image analysis. If you have any questions about the techniques seen here, or if you want to ask any question, just send me a note. I'd be glad to get back to you. Again, thank you for your interest in digital multimedia forensics.